This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
Math.PI is declared static final because the value of pi will never change for the life of the entire class. It will never change for any instance you make.
If you have a variable that won't change over the life of an instance of the class you could make that final but non-static. For example, if you have an Employee class, you could make the employeeId field (or anything that seldom changes) final, because it will be different for each instance but shouldn't change once it's been set.